System to control the quality of yarn and relative device

Abstract: System to control the quality of yarn in association with spinning machines or twisting frames, in which the yarn (12) cooperates with a yarn-guide loop (11) fitted solidly to an arm (14) which bears the yarn-guide loop (11) and which is secured to the structure of the machine, the system including at least one piezoelectric sensor (13) solidly fitted to the arm (14) bearing the yarn-guide loop (11), the piezoelectric sensor (13) being associated with a data processing and control means (17), which processes the signal generated by the piezoelectric sensor (13) and generates an electrical signal (16) of a sinusoidal type having an amplitude proportional to the tension of the yarn (12) and a frequency proportional to the speed of rotation of the balloon. Device to control the quality of yarn, which is suitable to be integrated in the system of the claims hereinbefore and comprises an arm (14) secured to the structure of the machine and bearing a yarn-guide loop (11) solidly fixed to the arm (14), the arm (14) being solidly associated lengthwise with a piezoelectric sensor (13).

Description: This invention concerns a system to control the quality of yarn and also a relative device, as set forth in the respective main claims. The system to control the quality of yarn according to the invention is applied advantageously to the textile field and, to be more exact, to single-twist or two-for-one twisting frames as well as ring spinning machines. The system to control the quality of yarn according to the invention enables anomalies to be detected and signalled in the yarn unwound from the twisting frame or spinning machine and the take-up of yarn on the yarn package or spindle to be halted. This invention can be applied to yarns made of any type of fibres, whether they be natural or manmade, continuous or discontinuous, of a staple length for wool or cotton. The invention can be employed on all existing textile machines and can be used for yarns of various materials and dimensions without being modified. In the spinning machines and twisting frames of the state of the art the yarn unwinding from the yarn package passes through a yarn-guide loop, which is generally located above and on the same axis as the spindle and has the task of limiting the balloon created by the centrifugal force generated by the rotation of the spindle. Devices have been disclosed which signal the breakage of the yarn with a view to providing a remote control of those machines. EP-A-0.436.204, which represents the closest prior art, discloses a device which includes loop-holder arms, all of which have a scanty rigidity with a vibrating part, the mass of which is out of proportion to the arm, so that the arm itself tends to start vibrating, and this situation could also lead to breakage. Moreover, the scanty consistency of the arms prevents them from keeping the loops aligned with the axis of the spindle inasmuch as they are unable to resist the strong stresses of the yarn passing through. In the case of two-for-one twisting frames various shortcomings may take place, such as the breakage of one of the yarns leading to the lack of the twisting operation, or else the union of undesired yarns whereby more yarns than those required are coupled together, or else the slipping of the spindle which causes a loss of twist in the yarn; or the belt setting the spindle in rotation may break with a resulting lack of twist in the yarn produced. The feeler devices of the state of the art do not enable these types of shortcomings to be identified and lead to the production of yarns of a low quality. Moreover, the feeler devices of the state of the art do not enable the inclusion of lumps in the unwinding yarn to be signalled, and therefore these lumps remain in the yarn produced, which is therefore of a low quality. The present applicants have designed, tested and embodied this invention to overcome the shortcomings of the state of the art and to achieve further advantages. This invention is set forth and characterised in the respective main claim, while the dependent claims describe variants of the idea of the main embodiment. One purpose of the invention is to provide a yarn quality control system which makes possible the detection and signalling of anomalies in the yarn such as even partial breakage of the yarn, unions of pluralities of yarns, loss of twist or complete lack of twist in the yarn produced. The system to control the yarn according to the invention enables also the inclusion of lumps in the yarn passing through to be detected. Furthermore, the yarn quality control system according to the invention may be combined with a yarn shearing device which is actuated automatically as soon as the yarn quality control system according to the invention detects one of the above anomalies. A further purpose is to achieve a yarn quality control system the sensor of which makes possible the detection of the speed of rotation of the balloon and of the tension of the yarn or yarns with which the sensor cooperates. In the device according to the invention the signal can be analysed not only as a presence or absence of a signal of detection of breakage of the yarn but also as regards its own characteristics such as amplitude and frequency in obtaining further information about the yarn or yarns running through the yarn-guide loop. In the yarn quality control system according to the invention these electrical signals generated by the mechanical vibration transmitted by the arm to the piezoelectric sensor are amplified and freed of spurious signals, thus providing a signal which is a function of the speed of rotation of the balloon and of the tension of the yarn running through. The electrical signal leaving the filter means is converted into impulses to control the speed of rotation and into voltage to control the tension of the yarn. On the one hand these impulses are examined by the control device and compared with a determined value of speed. If the average speed of rotation of the yarn varies beyond a given pre-set percentage determined as desired, a suitable signal is generated which actuates an acoustic and/or visual warning circuit or a stop signal. This same signal may also actuate a yarn shearing means which has the task of stopping take-up of yarn in the event of anomalies. On the other hand this signal is processed and examined so as to generate a signal which represents the average tension of the yarn. This average tension is processed to find its differential variations as compared to a pre-set value. If these differential variations of tension exceed a given threshold value, a suitable signal is generated which actuates an acoustic and/or visual warning circuit or a stop signal or else a signal to shear the yarn running through. If the signal is associated with an efficient enough filter means, it is also possible to detect the inclusion of lumps in the yarn running through and thus actuate the warning, stopping or shearing means. The attached figures are given as a non-restrictive example and show some preferred embodiments of the invention as follows:- Fig.1 is a block diagram of the method of working of the yarn quality control system according to the invention; Fig.2 shows diagrammatically the yarn quality control device according to the invention in association with a yarn package; Figs.3a and 3b show some embodiments of the yarn quality control device; Figs.4a and 4b show in an enlarged scale two cross-sections along the lines B-B and C-C respectively of a possible variant of the devices of Figs.3a and 3b. The reference number 10 in the attached figures denotes generally a device to control the quality of yarn according to the invention. The device described in the figures provides a yarn quality control device 10 having the task of a yarn-guide loop 11 and of a detector of anomalies in yarn 12 running through. The anomalies which can be detected by this yarn quality control device 10 may be various and may include a lack of yarn 12, a variation in the speed of rotation, a variation in the tension of the yarn 12, the inclusion of lumps in the yarn running through and the union of undesired yarns 12. This device provides a quality control device 10 which not only signals the presence of such anomalies but is also able to stop the take-up of yarn 12 when one or another of those anomalies occurs. The quality control device 10 according to the invention is used with a yarn 12 running in spinning machines or in single-twist or two-for-one twisting frames and makes possible the detection of loss of twist due to spindle slip 15 or of lack of twist in the yarn 12 owing to breakage of the transmission belt. Moreover, where the yarns are being produced with a plurality of yarns 12 twisted together, the yarn quality control device 10 according to the invention enables the lack of one of the yarns 12 and also the union of undesired yarns 12 to be detected. As is known, the yarn 12 leaving the spindle 15 in rotation is made to cooperate with the yarn-guide loop 11 located above and on the same axis as the spindle 15 so as to limit the balloon generated by that rotation. The yarn quality control device 10 includes at least one piezoelectric sensor 13 firmly associated with an arm 14 that bears the yarn-guide loop 11 (Fig.3a) so as to form a continuous extension of that arm 14. The piezoelectric sensor 13 is fitted firmly, and without additional connecting elements, to the arm 14 bearing the yarn-guide loop 11 and advantageously on the perimeter of, and along, that arm. As is known, the piezoelectric sensor 13 converts into electrical impulses the oscillations and vibrations generated by the yarn 12 running through the yarn-guide loop 11. The piezoelectric sensor 13 is connected by connecting cables 19 to a data processing and control means 17. So as to amplify the vibrations, the arm 14 bearing the yarn-guide loop 11 has advantageously a reduced cross-section coinciding with the piezoelectric sensor 13. In this case the reduced cross-section is provided by a narrowing notch 43, which may be on the same side as that to which the piezoelectric sensor 13 is fitted or on the opposite side and substantially corresponding to the lengthwise point of application of the piezoelectric sensor 13 (see Figs.3). The piezoelectric sensor 13 cooperates advantageously with a surface or hollow 18, which contains the sensor 13 lengthwise. According to a variant (Figs.4a and 4b) a plurality of piezoelectric sensors 13 are arranged on the periphery of the arm 14 according to two or more cartesian axes for instance so as to detect the oscillations of the yarn-guide loop 11 on different planes. In this example the piezoelectric sensors 13 are two in number arranged at 90° to each other and enable the oscillations of the yarn-guide loop 11 to be detected on two planes at a right angle to each other. In this case the arm 14 contains reductions of its cross-section or hollows 18 coinciding advantageously with the various piezoelectric sensors 13; these reductions of cross-section are associated with a coordinated series of notches 43 arranged in suitable positions with the piezoelectric sensors 13. These notches 43 are intended to accentuate the vibrations and oscillations of the yarn-guide loop 11 sensed by the piezoelectric sensors 13 and therefore to increase the sensitivity of the sensors 13. The piezoelectric sensor 13 generates an electrical signal 16, which is processed by an appropriate data processing means 17 which, in the event of anomalies, generates a warning signal 35a, as will be described better in the description that follows. In a first form of embodiment (Fig.3b) the arm 14 bearing the yarn-guide loop 11 includes at an intermediate lengthwise position a hollow 18 in which the piezoelectric sensor 13 is fitted. The piezoelectric sensor 13 is associated with connecting cables 19, which are connected to the data processing and control means 17. In this case the arm 14 contains an axial bore 20, through which the connecting cables 19 are passed. A covering element 21 consisting of a slidable sleeve 25 cooperates with the hollow 18 so as to protect the piezoelectric sensor 13 against any impacts. The slidable sleeve 25 includes positioning and clamping means 22, which in this case consist of an annular ledge 23 that cooperates with an annular groove 24 of a mating shape machined in the arm 14 bearing the yarn-guide loop 11 (Fig.3b). The forms of embodiment in Figs.3 show the narrowing notch 43 machined in the arm 14 on the opposite side to, and corresponding to, the hollow 18. In the form of embodiment of Fig.3a the covering element 21 consists of the sleeve 25, which has an outer diameter equal to the outer diameter of the arm 14 and cooperates with a mating seating 26 machined circumferentially in the arm 14 and corresponding with the hollow 18. In this case the sleeve 25 contains a separating slit 27 (Fig.4a) extending along its whole length so as to enable the sleeve 25 to be deformed and enlarged while being fitted to the arm 14. Fig.1 shows a possible working diagram of the control device 10 according to the invention; this is described in greater detail hereafter. The piezoelectric sensor 13 is stimulated by the oscillations and vibrations caused by the yarn 12 running through the yarn-guide loop 11; these vibrations and oscillations are transmitted by the yarn-guide loop 11 to the arm and thence, by transfer, to the piezoelectric sensor 13, which generates an electrical signal, which is amplified by an amplifier 28 and treated by a band-pass filter 29, which eliminates the noises of the mains frequency and the noises of high frequencies due to spurious oscillations of the yarn 12. The sinusoidal output signal 30 of the band-pass filter 29 is characterised by a frequency corresponding to the speed of rotation of the balloon and therefore of the spindle 15 and by an amplitude proportional to the tension of the sliding yarn 12. On the one hand the sinusoidal output signal 30 is converted into impulses by an impulse shaping means 31. These impulses are then counted and their value is compared with a value of rotation speed by a first comparator 32, which generates a speed differential signal 33 which is sent to a warning circuit 34. If this speed differential signal 33 exceeds a pre-set determined threshold value, the warning circuit 34 sends a first actuation signal 35a, which actuates an acoustic and/or visual alarm device 36 or a blocking device, which is not shown here. In this case the warning circuit 34 sends also a second actuation signal 35b, which actuates a yarn shearing means 37, which interrupts the take-up of yarn 12. On the other hand, the sinusoidal output signal 30 is converted into direct current voltage by a rectifier 38 equipped with a low pass filter 39, which enables the voltage fluctuations to be eliminated by generating a voltage signal 40 which represents the average tension of the yarn 12. The voltage signal 40 is then processed by a second comparator 41, which generates a voltage differential signal 42 that is sent to the warning circuit 34. If this voltage differential signal 42 exceeds a pre-set determined threshold value, the warning circuit 34 sends a first actuation signal 35a, which actuates the acoustic and/or visual alarm device 36 or a blocking device, which is not shown here. In this case the warning circuit 34 sends a second actuation signal 35b, which actuates the yarn shearing means 37, which interrupts the take-up of yarn 12.

Claims: Device to control the quality of yarn in association with spinning machines or twisting frames, in which the yarn (12) cooperates with a yarn-guide loop (11) fitted solidly to an arm (14), which bears the yarn-guide loop (11) and is secured to the structure of the machine, the system including a piezoelectric sensor (13) solidly fitted to the arm (14) bearing the yarn-guide loop (11), the piezoelectric sensor (13) being associated with a data processing and control means (17), which processes the signal generated by the piezoelectric sensor (13) and generates an electrical signal (16) of a sinusoidal type having an amplitude proportional to the tension of the yarn (12) and a frequency proportional to the speed of rotation of the balloon, the system being characterised in that the arm (14) includes a hollow (18) to which the piezoelectric sensor (13) is solidly fitted, the hollow (18) cooperating with a reduction of cross-section (43) to amplify the vibrations of the arm (14). Device according to Claim 1, in which, for controlling the speed of rotation, the data processing and control means (17) converts the electrical signal (16) into impulses which are counted and compared with a determined reference value, this comparison generating a speed differential signal (33) that conditions the speed of rotation. Device according to Claim 2, in which, when this speed differential signal (33) exceeds a given pre-set threshold, the data processing and control means (17) generates at least one actuation signal (35a, 35b). Device according to any of the preceding Claims, in which for controlling the tension of the yarn (12), the data processing and control means (17) converts the electrical signal (16) into voltage, this voltage being compared with a determined reference value so as to generate a voltage differential signal (42). Device according to Claim 4, in which, when the voltage differential signal (42) exceeds a given pre-set threshold, the data processing and control means (17) generates at least one actuation signal (35a, 35b). Device according to any preceding Claim, in which the hollow (18) is positioned longitudinally along a short extent. Device according to any preceding Claim, in which the arm (14) includes a covering and protective element (21) in correspondence with the piezoelectric sensor (13).

Inventors: LIANI MARIO, MARCON BRUNO, SAVIO PAOLO, LIANI, MARIO, MARCON, BRUNO, SAVIO, PAOLO
Applicants: ATEX SPA
Application year: 1994
Main classification: D01H13
IPC codes: B65H63, D01H13